The term "water-based functional fluid" is used herein to refer to water-based lubricants, hydraulic fluids, cutting fluids and the like. Water-based functional fluids are not a new concept. However, in recent times, the increasing cost and scarcity of petroleum has made it increasingly desirable to replace oil-based functional fluids with water-based functional fluids wherever possible. Other benefits can also flow from such replacements such as decreased fire hazard and environmental pollution problems. In many cases, however, it is not feasible to make such replacements because the water-based functional fluids cannot be modified in their properties so as to perform to the same high degree as their oil-based counterparts. For example, it has been often difficult, if not impossible, to replace certain oil-based hydraulic fluids with water-based fluids even though the desirability of doing so is evident.
One of the problems in formulating suitable water-based functional fluids has been the selection of thickening agents that provide the desired degree of thickening and at the same time are stable under high shear conditions. Various thickeners have been tried, but none have been found to be entirely acceptable. Among the thickeners that have been tried are the polysaccharides, cellulose ethers and esters, and various synthetic polymers. The polysaccharides include the natural gums such as gum agar, guar gum, gum Arabic, algin, the dextrans, xanthan gum and the like. The cellulose ethers and esters include hydroxy hydrocarbyl cellulose and hydrocarbyl hydroxy cellulose and their salts. Included in this group are hydroxyethyl cellulose and the sodium salt of carboxy methyl cellulose. The synthetic polymers include polyacrylates, polyacrylamides, hydrolyzed vinyl esters, water-soluble homo- and interpolymers of acrylamidoalkane sulfonates containing at least 50 mole percent of acryloamido alkane sulfonate and other comonomers such as acrylonitrile, styrene and the like. Others include poly-n-vinyl pyrrolidones, homo- and copolymers as well as water-soluble salts of styrene, maleic anhydride and isobutylene maleic anhydride, copolymers.
It has been suggested to use certain water-soluble hydroxy terminated polyoxyalkylenes as thickening agents. See, for example, U.S. Pat. Nos. 3,005,776; 3,346,501; 4,138,346; and 4,151,099. The degree of thickening provided by these polyoxyalkylenes has not, however, been found to be entirely acceptable.
U.S. Pat. No. 4,239,635 discloses carboxylic acid terminated diamides and alkali metal, ammonium or amine salts thereof which are derived from the reaction of organic polycarboxylic acids and polyoxyalkylene diamines. The reference indicates that these diamides have lubricating properties and are useful in aqueous metal working fluids.
U.S. Pat. No. 4,288,639 discloses the use of certain alpha-olefin oxide-modified polyoxyalkylenes as thickeners for aqueous liquids. This patent indicates that these thickeners are obtained by capping a liquid straight-chain polyoxyalkylene heteric or block copolymer intermediate with an alpha-olefin oxide.
There remains a need for water-dispersible thickening agents that can provide water-based functional fluids with desired levels of thickening and are sufficiently stable for high shear applications.